The present invention relates to a system for controlling a tab for an aircraft control surface.
It is known that in airplanes with mechanical controls, without servocontrols, it is commonplace to provide a tab on some of the aerodynamic surfaces of said airplane, such as the rudder, the elevators, the ailerons, etc. for example. Such tabs are intended to alter the maneuvering forces that the pilot would have to exert on the aerodynamic surfaces in order to turn them if tabs were not present.
Many works set out the ways in which these devices with tabs (the common name for such compensation flaps) work, as well as the equations governing their operation, and allow their characteristics to be calculated as a function of the application to the specific case. Among the more recent works, "Airplane Flight Dynamics and Automatic Flight Controls" by J. ROSKAM, published in the United States by Roskam Aviation and Engineering Corporation, 1979, may be mentioned.
In known compensation systems of the automatic type:
a tab is articulated so that it can rotate on the trailing edge side of the associated aerodynamic surface, itself mounted so that it can rotate on the structure of said aircraft (wing, stabilizer, empennage, etc.); PA1 the command (stick, wheel, rudder bar) available to the pilot of the aircraft is connected mechanically to said aerodynamic surface in such a way as to control the turning thereof with respect to said structure; and PA1 a mechanical linkage connects the tab to the structure in such a way that with each value of the angle through which said aerodynamic surface is turned with respect to the structure there corresponds, according to a determined relationship, a value of the angle through which the tab is turned with respect to said aerodynamic surface. PA1 a first sensor detecting the value of the angle through which said aerodynamic surface is turned with respect to said structure; PA1 a moving and controllable actuating member connected to said structure and capable of acting on said linkage to alter said determined relationship between the values of the angles through which said aerodynamic surface and said tab are turned; PA1 a second sensor detecting the position of said actuating member; and PA1 a control device receiving information from said first and second sensors and, on the basis of this information, formulating a command for said actuating member. PA1 in the first, on the basis of the information delivered by said first sensor, said control device generates a datum value for the position of said actuating member, this datum value depending on said parameter, and said command for the actuating member is the error signal of the difference between said datum value and the information delivered by said second sensor; PA1 in the second, on the basis of said parameter, said control device generates a datum value for the position of said aerodynamic surface and said command for the actuating member is the algebraic sum of the information from said second sensor and of said error signal of the difference between said datum value and the information delivered by said first sensor.
For the very reason that they are essentially mechanical, such known systems are unable to take account of all the parameters which would be needed to adapt the forces appropriately to all flight conditions. Their action cannot thus be optimum throughout the flight envelope and for any amount of turning whatever of the aerodynamic surface, because it necessarily has to come from a compromise. Some flight conditions, like those encountered if there was an engine breakdown or when rotating the airplane on takeoff, lead to the adoption of high levels of compensation in order to satisfy the regulations in force.
Moreover, the structural constraints during cruising flight at high speed will require a smaller amount of compensation, or even compensation in the other direction.
On the other hand, excessive compensation causes aerodynamic anomalies such as suction effects on the control surfaces for example.
In some cases, additional protection devices need to be introduced.